Conventionally, as a light-weight material for construct having heat resistance, fiber-reinforced plastics (hereafter referred to also as FRP) having various heat-resistant resins such as polyimide as a matrix have been developed mainly as a material for aerospace purposes. However, these heat-resistant resins such as polyimide are inferior in the formability and economy to epoxy resins for general purposes. For this reason, it has not been general to apply these heat-resistant resins, for example, to the field of vehicles, construction, and the like other than the materials for aerospace purposes.
Also, heat-resistant FRP using a phenolic resin, in particular a resol-type phenolic resin, is known in the art. However, these are produced by dehydration condensation of a resol-type phenolic resin with an acid catalyst, and are therefore porous to have insufficient strength.
On the other hand, an epoxy resin is excellent in formability and economy, and also has an extremely good adhesion property with carbon fiber, so that the epoxy resin has excellent characteristics as a matrix of FRP. However, conventional epoxy resins do not necessarily have sufficient heat resistance, and it has been difficult to ensure a high heat resistance of, for example, 250° C. or more.
In contrast to this, the present inventors have disclosed an epoxy resin composition made by compounding an ion-containing polymer into an epoxy resin (See, for example, Patent Document 1). In the above-mentioned patent document, an ion-containing polymer is used as a curing agent in an epoxy resin, and a cured product extremely excellent in heat-resisting property can be obtained. Namely, in the case of a polymer of a bi- or more-functional epoxy compound, a high cross-linking density polymer having a high uniformity of cross-linking with no scarcely cross-linked parts can be expected. Such an epoxy polymer may possibly exhibit a performance with physical properties not conventionally known in the art. It can be said that the use of such a polymer meets the demands of the relevant field of the art in which a further higher performance of an epoxy resin is needed in response to the technical innovation of the industrial field.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-204186